Protective system



April 18, 1939. o c. HOFFMANN 2,155,229

PROTECTIVE SYSTEM Filed Aug. 20, 1936 Inventor: Daniel C. Hoffmann,

i Attorn ey.

Patented Apr. 18, 1939 PATENT OFFICE rao'rsc'rrvn SYSTEM Daniel c. mam-in, Yeadon, Pa., asslgnors to General Electric Company, a corporation of New York Application August 20, 1936, Serial No. 97,003

My invention relates to protective systems "and Particularly to systems for protecting a direct current source against connection to a direct current load circuit when the polarity of the source is reversed, and its object is to provide an improved reverse polarity protective system of this My invention will be better understood from the following description when taken in connection with the accompanying drawing, the single fi ure of which diagrammatically illustrates a reverse polarity protective system embodyin my invention, and its scope will be pointed out in the appended claims.

connected to the load circuit 2. In accordance with my invention, I provide a simple arrangement for accomplishing this result. As shown in the drawing, the circuit breaker 3 is provided with a closing 'coil 4. the circuit of which is arranged to be completed by a relay 5 having an operating winding connected across the source of direct current i. In series with the winding of the relay 5, I connect a suitable impedance device 6 which has a high impedance relative to the impedance of the relay. Also in series with the winding of the relay 5, I connect suitable unidirectional conducting means I, such as a copper oxide rectifier, so as to conduct current to the winding of the relay 5 only when the direct current source I has a predetermined polarity.

In order to prevent the relay I from being operated to eflect the closing of the circuit breaker 3 in case the unidirectional conducting means 1 fails and becomes short-circuited, I also connect in parallel with the winding of the relay I suitable unidirectional means 0, which is connected so as to conduct current when the polarity of the source i is reversed with respect to said predetermined polarity. Therefore, if at *the time the unidirectional conducting means I fails, the

source i has the desired polarity, the relay 5 operates to close its contacts 9 and eflect the closing of the circuit breaker I to connect the source i. to the load circuit 2. However, it the source i has the opposite polarity at the time the unidirectional eonducting means I fails, the relay 5 does not close its contacts 9 because the current through the faulty unidirectional conducting means I is in a direction to flow through the unidirectional conducting means I and therefore the winding of the relay is short-circuited. The impedance device 0, under these conditions, limits the current through the two unidirectional conducting means to a safe value.

From the above description, it is evident that I have provided a simple arrangement for preventing .the circuit breaker 8 from being reclosed due to a failure of the unidirectional conducting means I at a time when the polarity of the source I is reversed.

While I have, in accordance with the patent statutes, shown and described my invention as applied to a particular system and as embodying various devices diagrammatically indicated, changes and modifications will be obvious to those skilled in the art, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

i. In combination, a source of direct current, a relay having a winding connected to said source, unidirectional conducting means connected in series with said winding, and means for preventing the operation of said relay when said unidirectional conducting means fails and the polarity of said direct current source is reversed including other unidirectional conducting means connected in parallel with said winding and arranged to conduct current in the opposite direction from that in which said first-mentioned unidirectional conducting means conducts current;

2. In combination, a source of direct current, a relay having a winding connected to said source, an impedance device connected in series with said winding, unidirectional conducting means connected in series with said winding, and means for preventing the operation of said relaywhen said unidirectional conducting means is short-circuited and the polarity of said direct current source is reversed including other unidirectional conducting means connected in parallel with said winding and arranged to conduct current in the opposite direction from that in which said first-mentioned unidirectional conducting means conducts current.

3. In combination, a source of direct current, a load circuit and polarity responsive means for eil'ecting the connection of said source to said load cimuit when said source has a predetermined polarity including a relay having a winding connected to said source, unidirectional conducting means connected in series with said winding and arranged to conduct current when said source has said predetermined polarity, and means for preventing the operation of said relay when said unidirectional conducting means fails and the polarity of said direct current source is reversed including other unidirectional conducting means connected in parallel with said winding and arranged to conduct current when the polarity of said source is reversed with respect to said predetermined polarity.

4. In combination, a source of direct current, a load circuit and polarity responsive means for effecting the connection of said source to said load circuit when said source has a predeteris reversed with respect to said predetermined polarity. DANIEL C. HOFFMANN. 

